Semiconductor device employing a method for forming a pattern using a crystal structure of a crystalline material

ABSTRACT

The present invention relates generally to a semiconductor device, and in particular, to a semiconductor device employing a method for forming a pattern for the formation of quantum dots or wires with 1˜50 nm dimension using the atomic array of a single or a poly crystalline material. The electron beam lithography method in accordance with the present invention uses the phase contrast atomic image of a single or a poly crystalline material itself.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a method for forming apattern and a semiconductor device, and in particular, to a method forforming a pattern for the formation of quantum dots or wires with 1˜50nm dimension using the atomic array of a crystalline material and to themanufacture of functional devices that have such a structure.

[0003] In the present invention, the functional device means anelectronic, magnetic, or optical device that can be fabricated byprocedures including the formation process of quantum dots or wires.

[0004] 2. Description of the Related Art

[0005] The formation process of quantum dots or wires becomes the coreprocess for the fabrication of an electronic, magnetic, or opticaldevice with quantum dots or wires as the application of such devices isincreasingly expected. A fundamental operating principle of such devicesis based on quantum mechanical results that the physical properties ofthe particle are greatly affected by its size as it becomesnanometer-sized. Particularly, there are many researches for the singleelectron transistor which has been suggested as the alternative to MOSdevice in order to overcome the limitation of the MOS device that hasbeen developed continuously for 40 years.

[0006] Previous researches on the formation processes of quantum dots orwires can largely be divided as follows.

[0007] First, there is a method in which one or a few quantum dots orwires are formed by AFM (Atomic Force Microscopy), STM (ScanningTunneling Microscopy) and electron beam lithography. This method has thecapability to form the quantum dots or wires whose size and location arecontrolled experimentally, but has difficulty in applying to massproduction because of a low throughput.

[0008] Second, there is a method in which quantum dots or wires areformed by the process of patterning and etching. In this method,patterning means the formation process of quantum dots or wires on thesubstrate by the electron beam direct-writing, or by the etching of thechemical substance which was imprinted by the mask or mold made with anelectron beam.

[0009] Third, there is a method in which quantum dots or wires areformed by the nucleation at the early state of phase transition ofmaterials. This method has can be applied to mass production, but hasproblems in controlling the size, density or distribution of quantumdots or wires.

SUMMARY OF THE INVENTION

[0010] Therefore, It is an object of the present invention to provide amethod for forming a pattern using a crystal structure of a material asa mask.

[0011] It is another object of the present invention to provide a methodfor forming quantum dots and wires of uniform size and density which canbe controlled by patterning a layer using a crystal structure of amaterial as a mask.

[0012] It is a further object of the present invention to provide amethod for forming quantum dots and wires using a crystal structure of amaterial for fabricating semiconductor devices in practice.

[0013] It is still another object of the present invention to provide asemiconductor device having the structure of quantum dots or wires.

[0014] The foregoing and other objects of the present invention can beachieved by providing a method for forming a pattern using a crystalstructure of a material as a mask. According to one aspect of thepresent invention, a method for forming a pattern using a crystalstructure of a material is comprising the steps of locating the materialhaving a crystal structure in the chamber of the transmission electronmicroscope; radiating an electron beam to the material; forming apattern from a lattice image of the material having a crystal structureon the surface of an irradiated material by diffracted electron beam andtransmitted electron beam passed through the material.

[0015] Preferably, the lattice image is formed by a method of the phasecontrast imaging.

[0016] Preferably, the material having crystal structure is processedinto a thickness of a few tens of nanometer.

[0017] Preferably, the irradiated material is a photoresist material ona semiconductor substrate.

[0018] Preferably, the semiconductor substrate has been applied withphoto-resist material after deposition of a gate oxide and an amorphoussilicon on the substrate in which source and drain regions are alreadyformed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0020]FIGS. 1A to 1C illustrate lattice points moved one-dimensional,two-dimensional, three-dimensional respectively.

[0021]FIG. 2 illustrates an arrangement of atoms around the latticepoint.

[0022]FIG. 3 illustrates the 7 crystal systems and the 14 Bravaislattices.

[0023]FIG. 4A illustrates a unit cell of crystal structure of Al.

[0024]FIGS. 4B to 4D illustrate two-dimensional projection patterns ofAl crystal through the [100], [110], [111] crystallographicorientations.

[0025]FIG. 5A illustrates a unit cell of crystal structure of Si.

[0026]FIGS. 5B to 5D illustrate two-dimensional projection patterns ofSi crystal through the [100], [110], [111] crystallographicorientations.

[0027]FIG. 5E illustrates a three-dimensional projection pattern whenFIG. 5C is rotated 56° clockwise and 15° azimuthally.

[0028]FIG. 6A illustrates a unit cell of crystal structure of GaAs.

[0029]FIGS. 6B to 6D illustrate two-dimensional projection patterns ofGaAs crystal through the [100], [110], [111] crystallographicorientations.

[0030]FIG. 6E illustrates a three-dimensional projection pattern whenFIG. 6C is rotated 56° clockwise and 15° azimuthally.

[0031]FIG. 7 is a schematic view of a first embodiment of TransmissionElectron Microscopy (TEM) according to the present invention.

[0032]FIG. 8 is a schematic view of a second embodiment of TEM accordingto the present invention.

[0033]FIG. 9 is a schematic view of a third embodiment of TEM accordingto the present invention.

[0034]FIGS. 10A to 10F are sectional views sequentially illustrating anembodiment of a process of fabricating single electron transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, preferred embodiments of the present invention willbe described in detail with reference to the accompanying drawings. Inthe following description, well-known functions or constructions are notdescribed in detail.

[0036] At first, to help understanding of the invention, crystalstructures of general materials and their various schematic figures willbe illustrated.

[0037] It is well known that the materials in the earth are composed ofatoms and molecules which contain a few atoms and particularly, solidmaterial is classified into a crystalline material in which the atomsare situated in a repeating or periodic array over large atomicdistances and an amorphous material that lacks a systematic and regulararrangement of atoms over relatively large atomic distances. Theresearch on the periodic array of the atoms started in 1912 by Max vonLaue who found x-ray diffraction. In 1913 W. H. Bragg and his son solvedthe crystal structure of diamond and salt by x-rays and in 1920 Ewaldintroduced the concept of the reciprocal lattice. Until now, the crystalstructures of more than a hundred thousand of organic or inorganiccompounds in the earth have discovered.

[0038] If a point is moved by the distance a parallel to a certaindirection, it matches second point and if that is moved the same way,that becomes third point. As the same way one point is moved parallelrepeatedly, an array of points is made as shown FIG. 1A. This array ofpoints which is generated with being repeatedly shifted at regulardistance along the given direction is called lattice. The motion ofshifting a point in this manner is called translation and expressed asvector a. Here regular distance, that is, the magnitude of the vector|a|=a is called period or unit period. In this array of points, eachpoint is the same and if one point is marked as an origin.

[0039] That is, r=ma where m is an integer from −^(∞) to ^(∞),

[0040] Point network plane is generated by translation this array ofpoints to the other direction as shown FIG. 1B and this is calledlattice plane. When this lattice plane is translated to translation c,the third direction which is not parallel to this plane, threedimensional point network plane is generated and called space lattice.In this space lattice, each lattice point is described by positionvector r from the origin and expressed as, r=ma+nb+pc

[0041] where, m, n, p are integers between −^(∞) to ^(∞). The spacelattice is infinitely spread in infinite space as shown FIG. 1C.

[0042] It is said that a crystal is macroscopically uniform, because theproperties of a part of crystal are the same as those of the other partat arbitrary distance away. FIG. 2 shows an imaginary crystal structure.A certain point p in this crystal is described by the position vector,L, and the unit translation vectors of this lattice a, b, c,$\quad\begin{matrix}{L = {{Xa} + {Yb} + {Zc}}} \\{= {{\left( {m + x} \right)a} + {\left( {n + y} \right)b} + {\left( {p + z} \right)c}}} \\{= {\left( {{ma} + {nb} + {pc}} \right) + \left( {{xa} + {yb} + {zc}} \right)}} \\{= {r + {r1}}}\end{matrix}$

[0043] where, X, Y, Z are real numbers and x, y, z are decimals between0 and 1. That is, a certain point in space is expressed by rl whichrepresents a crystal lattice, and r which represents position vector inthe lattice. Here, the unit lattice described by three translationvectors is called a unit cell.

[0044] When a certain point in the crystal is fixed as the origin(0,0,0), all lattice points generated from this point (0,0,0) areidentical with the origin and have the same properties. That is to say,whatever point is fixed as the origin in the crystal, every latticepoint made by translation from this point is identical. Identical meansall properties (including the geometric form of the surroundings aroundthis point, chemical properties such as a kind of neighbor atoms, orphysical properties such as electron density, potential difference) areexactly the same.

[0045] All crystalline includes one of the 7 crystal systems by therelation between three vectors, a, b, c that determine unit cell. TABLE1 shows the relation between lattice parameters which defines three axesof unit cell. TABLE 1 Crystal structure Crystal system Lattice parameterCubic Cubic A = b = c α = β = γ = 90° Hexagonal Hexagonal A = b ≠ c α= β= 90° γ = 120° Trigonal Rhombohedral A = b = c α = β = γ ≠ 90°Tetragonal Tetragonal A = b ≠ c α = β = γ = 90° OrthorhombicOrthorhombic A = b = c α = β = γ = 90°≠ Monocimic Monoclinic 1. c-uniquea ≠ b ≠ c α= β = 90° ≠ γ Monoclinic Monoclinic 2. b-unique a ≠ b ≠ c α=Δ = 90° ≠ β Triclinic Triclinic A ≠ b ≠ c α ≠ β ≠ γ ≠ 90°

[0046] Also all crystalline have one of the 14 Bravais lattices as shownin FIG. 3. It is classified according to the number of lattice points inunit cell as the primitive cell (P) has one lattice point in unit cell,the base-centered cell (A, B or C) has one lattice point in the centerof one plane, the face-centered cell (F) has lattice points in thecenter of each plane and the body-centered cell (I) has one latticepoint in the center of the unit cell.

[0047] The crystal structure, of which more than a hundred thousand oforganic or inorganic materials have been known until now, is classifiedas the 7 crystal systems and the 14 Bravais lattices. Actual crystalstructure is composed by the arrangement of one or more of the same ordifferent atoms in each lattice point which is included in the 14Bravais lattice.

[0048] Next, some examples of such a crystal structure are given and thepattern from the arrangement of atoms which is shown when those crystalstructures are projected to the given crystallographic orientation isexplained.

[0049] For example, Al is a cubic crystal system (a=b=c) and theface-centered cell of the Bravais lattices, so it has four latticepoints in one unit cell. The crystal structure of Al is made when one Alatom lies in one lattice point, and the lattice constant of Al isa=b=c=0.404 nm. Therefore the structure of Al unit cell is shown as FIG.4A. FIG. 4B, 4C, and 4D show the projection pattern of atomicarrangement through [100], [110] and [111] crystallographicorientations.

[0050] The other example is Si of a diamond crystal structure. Si iscubic crystal system and the face-centered of the Bravais lattices likeAl (Face Centered Cubic). So it has four lattice points in one unitcell, but it has two atoms in one lattice point unlike simpleface-centered cubic crystal system (lattice parameter a=b=c=0.543 nm).Therefore there are eight atoms in a Si unit cell. FIG. 5A shows theunit cell of Si. As the same way FIG. 5B, 5C and 5D show thetwo-dimensional projection pattern of atomic arrangement through [100],[110] and [111] crystallographic orientations. FIG. 5E shows the patternwhen FIG. 5B is rotated 56° clockwise and 15° azimuthally. As shown FIG.5C, the image looks like several lines. This is the evidence thatdepending on processing techniques, Si single crystal can apply to theform of quantum wires in a single electron transistor device.

[0051] And another example is the crystal structure of GaAs. GaAs has acrystal structure of cubic like Al and Si, and the face-centered Bravaislattice like Si. But, unlike Al of a simple cubic lattice and Si of adiamond crystal structure, GaAs has a crystal structure which is an oneGa atom and one As atom at one lattice point.(lattice parametera=b=c=0.565 nm) FIG. 6A shows the unit cell of crystal structure ofGaAs. By the same way, FIGS. 6B, 6C, 6D are two-dimensional projectionpatterns of GaAs crystal through the [100], [110], [111]crystallographic orientations. FIG. 6E shows the pattern when FIG. 6C isrotated 56° clockwise and 15° azimuthally in the same manner of FIG. 5E.Like Si, the single crystal of GaAs is a good example applicable to thequantum wire formation.

[0052] Al, Si, and GaAs mentioned above are only a few examples amongthe already known crystal structures over a hundred thousand. Thus,these demonstrations indicate that very various patterns generated byelectrons transmitted in the two dimensional plane can be obtained. Ofcourse, this generated pattern is dependent on the crystallographicorientation as well as on the crystal structure.

[0053] The atom's array of the crystal can be observed using thephase-contrast method in high resolution TEM (transmission electronmicroscopy). As the electron microscopy has developed, it is possible todistinguish the atoms alignments with the range of 0.14 nm-0.20 nm under200 kV-300 kV of an accelerating voltage.

[0054] In the phase contrast method, atomic images can be made by thephase difference between diffracted electron beam and transmittedelectron beam which is generated from the crystal material. This methodhas a much better resolution than other methods such as a diffractioncontrast or an absorption contrast.

[0055]FIG. 7 shows how an interference image is made by the phasedifference. As shown in FIG. 7, the image is formed by the phasedifference between diffracted electron beams and transmitted beams inthe plane of projection.

[0056] The material (5) with the thickness of a few tens of nanometer isputted in a chamber. Electron beam (3) can transmit this kind of thickmaterial (5). At the same time, the interaction between the material (5)and the transmitted electrons cause the electron beam separated todiffracted beams and transmitted beams.

[0057] Transmitted beam and diffracted beam, which were separated duringthe transmission through the material (5), pass an objective lens (7)and an aperture (8). As a result of the interference with these twobeams, the lattice image of crystal structure is formed. In the presentinvention, the image plane means the plane where transmitted beam anddiffracted beam make the lattice image of a crystal structure by theirinterference during the transmission of material (5). This image formedin the image plane (9) can be magnified, used as it is or contracted bythe lens. In the present invention, the pattern is formed using thisimage.

[0058] The distance of the interference fringe is proportional to thespacing of lattice, which is the distance between atoms. As a result,the atomic array can be distinguished by this interference pattern.

[0059] In fact, in the practical high resolution TEM, the firstinterference image which is formed by the objective lens is magnifiedsequentially by other lens which is located behind the objective lens.As a result, this image which is magnified by several hundreds ofthousand can be observed directly. In general, magnification of anobjective lens is the range from several decades to several hundreds.For example, when the magnification of an objective lens is one hundred,3 nm spacing of atomic array is magnified into 30 nm that is a spacingof interference image. When this interference image is magnified or downscaled again by other lens, the image of atomic line and atoms with therange from a few nm to a few tens of nm will be obtained.

[0060] The present invention is intended to make the pattern by usingthe crystal structure of materials. The electron beam is radiated to thesample material which has a crystal structure and is loaded in thechamber. When the electron is transmitted through this sample, thelattice image is formed by the phase contrast method. The phase contrastis generated by the interference between the transmitted electron beamand the diffracted electron beam. By using this lattice image of thecrystal structure, the pattern for the fabrication of the functionaldevice can be obtained.

[0061] In this embodiment, method for forming a pattern using a crystalstructure of a material is to fabricate the semiconductor devices, byplacing a material having a crystal structure in the chamber of the TEM,irradiating electron beam, then, forming a lattice image of thatmaterial by a method of the phase contrast imaging, and finally formingthe pattern in the semiconductor substrate from a lattice image of thematerial having a crystal structure.

[0062] In the present invention, the method to fabricate the pattern isas follows. The lattice image which is formed in the image plane ismagnified or down-scaled to the intended size. Then, this image canexpose the photoresist which is applied on the semiconductor materials.This image can be formed by using some parts of the lattice image of thesample material loaded in the chamber.

[0063] In the high resolution TEM that is used currently, the resolutionof the atomic scale is already guaranteed. Therefore, in a method forforming a pattern introduced in the invention, if lattice images of acrystal structure that is formed at the imaging plane is scaled downinstead of scaling up, then semiconductor substrate that is applied withthe photo resist is exposed to this image. As a result, it is possibleto form patterns of a few angstrom on the semiconductor wafer.

[0064] The shape of the pattern, which is formed by using a crystalstructure of a material by a method of the invention, is determined by acrystal structure of the material used. Therefore, the location of atomsand distances of the atoms in a crystal structure of a material isembodied in the final semiconductor device as it is shaped.

[0065]FIG. 8 shows another example of the present invention.

[0066] As shown in FIG. 8, the material that is processed into thesample with a thickness of a few tens of nanometer (13) is placed at thecenter of the chamber in order to be passed through by the electron beam(11). The electron beam (11) is split into diffracted beam andtransmitted beam by the interaction with the material (13) which have acrystal structure.

[0067] Transmitted beam and diffracted beam, into which the incidentbeam is split during the transmission through the material (13), pass anobjective lens (15) and an aperture (17). As a result of theinterference with these two beams, the lattice image of crystal

[0068] structure is formed. In the present invention, the image planemeans the plane where transmitted beam and diffracted beam make thelattice image of crystal structure by their interference during thetransmission of material (13). The intermediate lens (19) magnifies theimage, which is formed at the image plane.

[0069] In the present invention, spacing of the atomic plane of amaterial, alignment of the electron beam, the degree of vacuum in thecolumn of the TEM, the degree of correction of a astigmatism, and thebrightness of the electron gun determine the accelerating voltage.Generally, the current accelerating voltage is the range from 100 keV to1 MeV. If the spacing of the atomic plane is about 3 angstrom, theaccelerating voltage of the 100 kV is used, and if the spacing of theatomic plane is about 2 angstrom, the accelerating voltage of the 200 kVis required.

[0070] The single electron transistor device, which is fabricated by amethod of the invention, has the structure that is constituted by asemiconductor substrate, a source region that is formed in thesemiconductor substrate, a drain region spaced from the drain region inthe semiconductor substrate, and a layer that includes quantum dots.These quantum dots are placed on the semiconductor region locatedbetween the drain region and the source region and have the same patternwith the lattice image of the material in the chamber

[0071]FIG. 9 shows another example of the present invention.

[0072] As shown in FIG. 9 the sample material (23) of a few tens ofnanometer is placed at the center of the chamber in order to be passedthrough by the electron beam (21). The electron beam (21) is split intodiffracted beam and transmitted beam by the interaction with thematerial (23) which has a crystal structure.

[0073] Transmitted beam and diffracted beam, into which the incidentbeam is split during the transmission through the material (23), pass anobjective lens (25) and an aperture (27). As a result of theinterference with these two beams, the lattice image of crystalstructure is formed. In the present invention, the image plane means theplane where transmitted beam and diffracted beam make the lattice imageof crystal structure by their interference during the transmission ofthe material (23). The intermediate lens (29) can reduce the image,which is formed at the image plane.

[0074]FIGS. 10A to 10F are sectional views sequentially illustrating anembodiment of a process of fabricating a single electron transistor.

[0075]FIG. 10A illustrates the steps of forming a source (31) and adrain region (33) in Si wafer.

[0076]FIG. 10B illustrates the steps of growing a gate oxide film (35)of a few nm thickness on the Si wafer and depositing the amorphous Si(37) of a few nm thickness on the gate oxide (35).

[0077]FIG. 10C illustrates the steps of coating photo-resist (39) on theamorphous Si (37).

[0078] Then place a silicon having [110] zone axis in the TEM chamber toform the pattern as shown in FIG. 5E.

[0079]FIG. 10D illustrates the steps of radiating the electron beam toexpose the photo-resist film (39).

[0080]FIG. 10E illustrates the steps of removing the photo-resist film(37), and etching the amorphous silicon (37) using the plasma process toform quantum dots.

[0081]FIG. 10F illustrates the steps of depositing control oxide (41)and poly-silicon (43) on the amorphous silicon (37) on that regionformed quantum dots and then patterning. As a result, the singleelectron transistor device is fabricated

[0082] In the fabricated device, the pattern of quantum dot that is madeon the gate oxide (35) is the same with the pattern of Si, which has[110] zone axis. The size of quantum dot is 5 nm, and the density isabout 1012/cm².

[0083] In accordance with the present invention as described above, thequantum dots can be formed and controlled using the lattice image of acrystal structure.

[0084] While the present invention has been described in detail withreference to the specific embodiments, they are mere exemplaryapplications. Thus, it is to be clearly understood that many variationscan be made by anyone skilled in the art within the scope and spirit ofthe present invention.

1-12. (canceled)
 13. A semiconductor device, comprising: a semiconductorsubstrate, a source region located in said semiconductor substrate; adrain region spaced apart from said source region and located in saidsemiconductor substrate; a quantum dot layer formed by patterning a gatelayer on a semiconductor substrate region which is located between saidsource and drain region wherein said patterning comprises a method forforming a pattern using a crystal structure of a single or a polycrystalline material, comprising the steps of: locating said materialhaving a crystal structure in a chamber; radiating an electron beam tosaid material in said chamber; forming a pattern from a lattice image ofsaid material formed as a result of interference between diffracted beamand transmitted beam passed through said material on the surface of anelectron beam resist on said gate layer.
 14. The semiconductor device ofclaim 13, wherein said material having a crystal structure has athickness of a few tens of nanometer.
 15. The semiconductor device ofclaim 13, wherein a gate oxide film exists between said quantum dotlayer and said semiconductor substrate.
 16. The semiconductor device ofclaim 13, wherein a control oxide layer is deposited on said quantum dotlayer.
 17. The semiconductor device of claim 13, wherein said gate layeris formed of an amorphous Si.
 18. The semiconductor device of claim 16,wherein a polycrystalline Si layer is deposited on said control oxidelayer.
 19. A semiconductor device, comprising: a semiconductorsubstrate, a source region located in said semiconductor substrate; adrain region spaced apart from said source region and located in saidsemiconductor substrate; a quantum dot layer formed by patterning a gatelayer on a semiconductor substrate region which is located between saidsource and drain region wherein said patterning comprises an electronbeam lithography method for forming a pattern using a crystal structureof a single or a poly crystalline material, comprising the steps of:providing a film of electron beam resist on said gate layer; irradiatingan electron beam to said material in a chamber; forming a pattern from alattice image of said material formed as a result of interferencebetween a diffracted beam and a transmitted beam passed through saidmaterial on said film of electron beam resist on said gate layer. 20.The semiconductor device of claim 19, wherein said material having acrystal structure has a thickness of a few tens of nanometer.
 21. Thesemiconductor device of claim 19, wherein said lattice image of materialis formed by a method of the phase contrast imaging.
 22. Thesemiconductor device of claim 19, wherein said material having a crystalstructure is Si.
 23. The semiconductor device of claim 19, wherein saidgate layer is formed of an amorphous Si.
 24. The semiconductor device ofclaim 19, wherein a gate oxide film exists between said quantum dotlayer and said semiconductor substrate.
 25. The semiconductor device ofclaim 19, wherein a control oxide layer exists on said quantum dotlayer.
 26. The semiconductor device of claim 25, wherein apolycrystalline Si layer is deposited on said control oxide layer.
 27. Asemiconductor device, comprising: a semiconductor substrate; a sourceregion located in semiconductor substrate; a drain region spaced apartfrom said source region and located in said semiconductor substrate; aquantum dot layer formed by patterning a gate layer on a semiconductorsubstrate region which is located between said source and drain regionwherein said patterning comprises an electron beam lithography methodfor forming a pattern using a crystal structure of a single or a polycrystalline material, comprising the steps of: providing a film ofelectron beam resist on said gate layer; irradiating an electron beam tosaid material in a chamber; forming a pattern from a lattice image ofsaid material formed as a result of interference between a diffractedbeam and a transmitted beam passed through said material on said film ofelectron beam resist on said gate layer, patterning said film ofelectron beam resist on said gate layer.
 28. The semiconductor device ofclaim 27, wherein said lattice image of material is formed by a methodof the phase contrast imaging.
 29. The semiconductor device of claim 27,wherein said material having a crystal structure has a thickness of afew tens of nanometer.
 30. The semiconductor device of claim 27, whereinsaid electron beam lithography method further comprises passing saiddiffracted beam and said transmitted beam through an aperture prior tosaid step of forming said pattern.
 31. The semiconductor device of claim27, wherein said gate layer is formed of an amorphous Si.
 32. Thesemiconductor device of claim 27, wherein a gate oxide exists betweensaid quantum layer and said semiconductor substrate.